Central impression printing presses, which have been used for many years, are characterized by a central impression cylinder with a plurality of print stations spaced around the central impression cylinder. Each print station typically includes a meter roll, an anilox roll, and a print roll. These types of printing presses are preferred because they maintain relatively precise registration of the printed material. Typical central impression presses include three to eight print stations and have a web width ranging from approximately four to sixty inches. To support the central impression cylinder and the print stations while maintaining registration with the desired precision, central impression presses utilize substantially fixed and continuous opposing side walls to support the central impression cylinder and the print stations. The side walls typically enclose the sides of the print stations thereby substantially inhibiting access to the central impression cylinder and the print stations.
At several points during a printing process and at the conclusion of a printing job, the printing press operator must clean and/or change the rolls in one or more of the print stations. In currently available central impression presses, it takes an inordinate amount of time to remove the anilox and meter rolls for cleaning or replacement with different rolls for a different job. Because it takes so long to remove the rolls for cleaning or to change the rolls, operators are encouraged to risk potentially severe injury by cleaning the rolls while they are still in the press, and occasionally operators sacrifice print quality by not changing the rolls when required for the next printing job.
More specifically, when cleaning the rolls while in the press, operators risk pinching their fingers between rolls. To clean rolls around their entire circumference, operators jog, that is incrementally rotate, the rolls or leave the rolls rotating while holding a cloth against the roll with their hands. As expected, cloths and fingers occasionally get caught between rolls, and when a finger gets caught, the finger is severely injured or even lost. As to print quality, cleaning the rolls with cloths is not as effective as rinsing them in wash basins. Also, anilox rolls are provided with different cell configurations and concentrations to control the amount of ink that is transferred to the print roll for application to the web which passes between the central impression cylinder and the print rolls. If the anilox roll already in the press is close in cell configuration and concentration to the anilox roll required for the next print job, operators are tempted to save time by using the anilox roll from the previous print job thereby diminishing the print quality.
Doctor blades are also used to further improve print quality by more accurately metering the amount of ink transferred to the print rolls. The doctor blades scrape against the anilox rolls to remove excess ink. For doctor blades to be effective, they must be positioned between the meter rolls and the print rolls to scrape the anilox rolls after they are inked by the meter rolls and before the anilox rolls transfer their ink to the print rolls. For print stations on the downstream side of the central cylinder, the doctor blades are positioned opposite to the central cylinder, but for print stations on the upstream side of the central cylinder, the doctor blades must be positioned between the print station and the central cylinder. Thus, the upstream doctor blades would be inaccessible to an operator making it commercially unfeasible to use doctor blades on upstream print stations.